1. Technical Field
The present invention relates to a magnetic coupling type isolator having a magnetic field generator and a magnetoresistive element such as a TMR (tunneling magnetoresistance) element, a CIP-GMR (current-in-plane giant magnetoresistance) element, and CPP-GMR (current perpendicular-to-the-plane) element.
2. Related Art
In an electronic circuit, for example, if a portion where a large current flows and a portion where a signal is transmitted are approximated to each other, the portion where a large current flows may influence signal transmission. For this reason, a circuit element for electrically separating the portion where a large current flows from the portion where a signal transmission is performed is necessary. Such a circuit element includes an optical isolator using a photo-coupler. The optical isolator includes a combination of a light sensing element and a light emitting element and has a function of transmitting signals by converting electricity into light and vice versa.
Meanwhile, a magnetic coupling type isolator capable of providing further miniaturization and lower power consumption compared to the optical isolator has been developed. For example, PCT Japanese Translation Patent Publication Nos. 2000-516714 and 2003-526083 disclose a magnetic coupling type isolator having a magnetic field generator for converting an input signal into a magnetic field and a magnetoresistive element for detecting the external magnetic field generated by the magnetic field generator and converting it into the electric signal. Here, the magnetoresistive element includes a Hall element, an AMR (anisotropic magnetoresistive) element, or a GMR (giant magnetoresistive) element.
In the magnetic coupling type isolators disclosed in PCT Japanese Translation Patent Publication Nos. 2000-516714 and 2003-526083, a shield capability for unnecessary magnetic fields from an external environment is obtained by providing a shield film in an upper portion of a coil where the magnetic fields are generated. This shield film also functions as a concentrator of the magnetic fields applied to the magnetoresistive element from the coil.
However, in the magnetic coupling type isolators disclosed in PCT Japanese Translation Patent Publication Nos. 2000-516714 and 2003-526083, the shield film is disposed only in the coil. Therefore, it may be impossible to obtain a sufficient tolerance to the external magnetic fields or an EMS (electro magnetic susceptibility).